1. Field of the Invention
This invention relates to the preparation of alpha-olefin copolymers and more particularly to the preparation of alpha-olefin copolymers having improved hydrocarbon oil pipeline friction-reducing properties.
2. Prior Art
When fluids are pumped through a conduit, such as a pipeline, friction resulting from the movement of the fluid over the inside surface of the conduit causes a pressure drop in the fluid which increases as the downstream distance from the pump increases. The pressure drop results in reduced flow rates. It is known that the flow rate of the fluid through the conduit can be increased by reducing the friction of the fluid in the conduit.
Hydrocarbon fluid frictional loss in conduits can be reduced by injecting into the fluid polymeric substances which are capable of reducing the friction loss of the fluid moving through the conduit. It has been reported that alpha-monoolefin polymers are particularly useful for reducing friction loss in hydrocarbons such as crude oil flowing through pipelines. U.S. Pat. No. 3,692,676 discloses the reduction of friction loss in hydrocarbon liquids flowing through pipelines by adding to such liquids small amounts of homopolymers or copolymers of alpha-olefins having from 6 to 20 carbon atoms. U.S. Pat. Nos. 3,351,079; 3,493,000; 3,559,664 and 3,682,187, disclose the addition of polyethylene or copolymers of ethylene and propylene or other low molecular weight alpha-monoolefins to hydrocarbon fluids to reduce fluid friction loss. U.S. patent application Ser. No. 230,775 filed Feb. 2, 1981 now abandoned discloses the addition of copolymers of butene-1 and at least one other alpha-monoolefin to a hydrocarbon fluid flowing in a pipeline to reduce frictional loss. The specifications of the above patents and patent application are incorporated herein by reference.
Even though such additives may effect drag reduction in hydrocarbon liquids flowing through conduits their use is expensive because of their high costs and the large quantities of them required in continuous use applications. Accordingly, improvements which lower the cost of use of these drag reducing agents, such as increasing their efficiency, are continuously sought.
U.S. Pat. Nos. 2,976,271 and 2,983,720 disclose the polymerization of propylene and butene-1, respectively, by means of a three component catalyst comprised of aluminumtrialkyl, aluminumdialkyl monohalide and a reducible compound of titanium, such as titanium tetrachloride. U.S. Pat. No. 2,971,925 discloses the preparation of polymers of monoolefins having a high degree of linearity by polymerizing monoolefins in the presence of catalyst prepared by reacting aluminumtriethyl and titanium tetrachloride and reacting the resulting product with a hydrocarbon solution of aluminumdiethyl chloride. U.S. Pat. No. 2,943,063 discloses the polymerization of olefins in the presence of a catalyst comprised of combinations of titanium tetrahalide with trialkylaluminum or dialkylaluminum halide. U.S. Pat. No. 3,222,295 discloses the preparation of monoolefin polymerization catalysts by reacting a titanium tetrahalide with a dialkylaluminum halide and reacting the resulting complex with an aluminumtrialkyl compound. U.S. Pat. Nos. 3,257,368, 3,261,821 and 3,281,375 teach the preparation of alpha-monoolefin polymers by a catalyst prepared by reacting a solution of aluminumtriethyl and titanium tetrachloride with aluminumdialkyl halides. U.S. Pat. No. 3,723,350 discloses olefin polymerization catalysts made by reducing a mixture of metallic halides, including a titanium tetrachloride with a dialkylaluminum halide and reacting the reduction product with an aluminumtrialkyl, an alkylaluminum halide and/or a dialkylaluminum halide.
The above references show the use of trialkylaluminum compounds and dialkylaluminum halides alone or in combination as activators for alpha-monoolefin catalyst polymerizations. It has been observed that trialkylaluminum activators used alone increase the rate of Ziegler catalyzed polymerization of alpha-monoolefins, but the drag reducing effectiveness of the resulting polymers is relatively low. On the other hand the drag reducing effectiveness of alphamonoolefin copolymers prepared with a Ziegler catalyst activated solely by a dialkylaluminum halide is better than those obtained using trialkylaluminum as the sole activator but the rate of polymerization of the former products is relatively low.